Muffler



0. E. BLAIR MUFFLER Nov. 22, 1960 2 Sheets-Sheet 1 Filed Oct. 28, 1958 Nov. 22, 1960 o. E. BLAIR 2,961,059

MUFFLER Filed Oct. 28, 1958 2 Sheets-Sheet 2 inert/817:} 0

United States Patent MUFFLER Orby E. Blair, Hawthorne, Calif., assignor to Northrop Corporation, a corporation of California Filed Oct. 28, 1958, Ser. No. 770,102

1 Claim. (Cl. 181-56) This invention relates to sound suppressors and more particularly to mufilers for internal combustion engines and the like.

The instant muffler was developed during a program initiated to provide a suitable sound suppressor for the internal combustion engines of helicopters. To the best of applicants knowledge rnufilers or other types of sound suppressors have not been utilized to suppress the noise originating with internal combustion engines mounted in helicopters. The non-use of mufilers on helicopter engines is unquestionably due to space limitations within the engine compartment.

During the aforementioned development program it was discovered that the muffler as disclosed herein displayed superior attenuating characteristics not found in mufllers now available. Numerous theories have been advanced as to why the instant muffler is more effective as a sound suppressor than conventional rnufilers of a similar type especially throughout certain frequency ranges. Inasmuch as these theories are not in complete agreement a discussion thereof will not be given in this specification. However, as the specification progresses it will be shown that the instant mufiler structure does provide superior attenuating characteristics which conventional types of mufllers do not provide.

It is an object of this invention to provide a mufller for internal combustion engines having superior attenuating characteristics as compared with conventional type muffiers.

Another object is to provide a muffler that is extremely simple and compact in design and construction and is economical to manufacture.

Although the characteristic features of the present invention are particularly pointed out in the appended claim, the invention itself, also the manner in which it may be carried out, will be better understood by referring to the following description taken in connection with the accompanying drawings forming a part of this application and in which:

Figures 1 and 2 are side and end views, respectively, of the mufiler disclosed herein. In Figure 1 portions of the mufiler are broken away to show the internal construction thereof.

Figure 3 is a sectional view, the view being shown on an enlarged scale of the mufller as it appears when viewed along the line 3-3 of Figure 1.

Figure 4 is a graphical showing of the attenuation characteristics of the instant mufiler as compared with an available muffler designed by National Advisory Committee for Aeronautics (NACA).

Referring now to the drawings, a mufiler structure of the type disclosed herein is shown in Figures 1 and 2 and is identified in its entirety by the numeral 11. The muffler 11 includes a body portion 12, a pair of inlet ducts 1 41-4 and an exhaust duct 16.

The body portion 12 comprises an elongated tubular section 17, which is circular in cross-section, a pair of disc-like end plates 18-18 and a pair of disc-like baflie ice plates 1919. The baffie plates 1919 have four apertures 21 formed therein which are equally spaced and positioned in the plates 19 substantially as shown in Figure 3. A strengthening rib 22 is welded to one of the side surfaces of each of the plates 19 and extends diametrical across the plates at locations between the ports or apertures 21. The end plates 1818 are circular in plan and have a concavo-convex configuration.

The end plates 18-18 are secured in the respective ends of the tubular section 17 in fluid tight relation with their convex portions extending outboard a slight distance beyond the ends of the section 17 substantially as shown in Figure 1. As assembled the section 17 and end plates 18-1S cooperate to define an exhaust chamber 23. The baflle plates are secured in the section 17 and extend in a direction normal to the longitudinal axis A of the section 17 to divide the chamber 23 into a center and a. pair of outboard sub-chambers, all of the sub-chambers being of substantially equal length and volume.

The exhaust duct 16 is circular in cross-section and includes a straight section 24 which extends through the wall of the section 17. The section 24 extends a short distance, approximately one-half the radius of the section 17, into the chamber 23. The location of the section 24 is further characterized in that it is offset laterally with respect to the axis A and longitudinally with respect to the mid-point of section 17 and is canted in two directions with respect to first and second reference planes 20 and 25, respectively. In Figures 1 and 2 the reference planes 2% and 25 are vertical and horizontal, respectively, and their intersection coincides with the axis A.

The point of entry of the section 24 into the chamber 23 is offset a distance X with respectto the mid-point of section 17. The distance X is approximately equal to one-quarter of the longitudinal extent of one of the subchambers comprising the exhaust chamber 23. Laterally the point of entry of the section 24 is ofiset a distance Y with respect to the axis A. The distance Y is approximately equal to four-fifths of the radius of the section 17. The relation of the section 24, with respect to the section 17, is also characterized in that it is canted with respect to the aforementioned vertical and horizontal reference planes by angles or and 5, respectively, substantially as shown in Figures 1 and 2. These angles a and [3 are of a magnitude of approximately 30 and 60, respectively.

The inlet ducts 1414 are of arcuate configuration when considered in a lengthwise sense and are circular in cross-section. They extend through the wall of the section 17 at locations adjacent the end plates 1818. The relation of the ducts 1414, with respect to the section 17, is further characterized in that they are located equal distances Z on opposite sides of the vertical reference plane. The respective distances Z are equal to approximately one-third of the radius of the section 17. The inlet ducts are also canted inboard laterally and longitudinally of the section 17, that is in the direction of the mid-point of the section 17, as indicated by the angles w and 5, respectively, which angles (7 and 6) are approximately 60. The ducts 14-14 also extend a short distance, approximately equal to one-half the radius of the section 17, into the chamber 23 and terminate in respective outboard sub-chambers.

The construction of the rnufiier 11 having been described a discussion of the acoustical properties of the instant muffier, with respect to the aforementioned NACA designed mufiier, follows.

Referring to Figure 4 the attenuation characteristics of NACA mufller (Configuration No. 59) is graphically compared to the attention characteristics of mufiler 11. The construction of the NACA muffler (Configuration No. 59-descri'oed and illustrated in NACA Tn No. 1838, dated March 1949) is similar to the mufiler 11, however,

the NACA mufiler does not incorporate the novel features disclosed therein. In Figure 4 noise attenuation is plotted against noise frequency (c.p.s.); the solid curve depicts the actual noise attenuation of the NACA muflier while the broken line represents the actual noise attenuation of the mufiler 11. From the comparative graph of Figure 4 it will be seen that in the frequency range below 200 c.p.s. both mufiiers follow very nearly the same curve. In the frequency range between 200-300 c.p.s. the NACA mufiler has an 8 to 10 decibel advantage over the muffler 11. At frequencies higher than 300 c.p.s. the NACA mufller offers practically no attenuation, in fact it provides severe ampliation around 400 c.p.s., while the mufller 11 achieves its greatest noise attenuation in this area. The latter area (above 300 c.p.s.) represents the range in which an internal combustion engine normally operates and certainly is the range of an engine mounted in a. helicopter during its cruise period.

It should be understood that negative attenuation, shown as occurring in connection with the NACA muffler at frequencies between 300-500 c.p.s. in Figure 4, does not imply the generation of sound within the mufiler, but simply that the mufller provides a less favorable terminal impedance to the exhaust pipe than an open pipe, that is an exhaust pipe without a muffler, ofiers.

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed cornprise a preferred form of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claim.

What is claimed is:

A muflier for internal combustion engines and the like comprising: a body structure including side and end walls secured together to provide a cylindrical exhaust chamher; the longitudinal axis of said exhaust chamber coinciding with the intersection of first and second reference planes having a nonnal relation with respect to each other; a pair of apertured baffle plates mounted in said body structure dividing said exhaust chamber into a cylindrical center sub-chamber and a pair of cylindrical outboard sub-chambers located respectively at each end of said center sub-chamber; a pair of inlet ducts extending through the side walls of said body structure in fluid tight relation; the location of said inlet ducts being characterized in that they are canted inboard to exhaust gases flowing therethrough toward the geometric center of said exhaust chamber, they are located on opposite sides of said first reference plane and their inner ends terminate respectively in said outboard sub-chambers; an outlet duct extending through the side wall of said body structure in fluid tight relation with the inner end thereof terminating in said center sub-chamber: said outlet duct being oifset laterally and longitudinally with respect to the longitudinal axis and geometric center, respectively, of said exhaust, chamber; and said outlet duct being canted with respect to said first and second reference planes.

References Cited in the file of this patent UNITED STATES PATENTS Tyskewicz Apr. 26, 1949 Maxim Oct. 19, 1954 OTHER REFERENCES 

